The major objective of this work is the application of digital computers to the derivation of synthetic pathways to complex organic structures. A general problem-solving program, LHASA II (Logic and Heuristics Applied to Synthetic Analysis), is being developed which can be used interactively by a chemist with simple graphical input-output of structural formulas. The principles and strategies of organic synthesis are being formalized for use by the program. In addition, the vast range of information on synthetic chemistry is being organized and rationalized to provide a rich and effective data base. The program will be applied to key problems involving biologically important substances and eventually will be made available for general use.